Objective: To evaluate the effect of material type and bonded substrate on the marginal and internal adaptation of occlusal veneer restorations. Materials and methods: Ninety intact human mandibular molars were selected for this study, divided into three groups (N= 30) depending on three different martials of lithium disilicate ceramic (L), zirconia (Z) and hybrid ceramics (H) with the thickness of 1.0 mm. Each test groups divided into three subgroups (N=10) depending on the bonded substrate, subgroups (LD, LC and LF), subgroups (ZD, ZC and ZF) and subgroups (HD, HC and HF). Before cementation, discrepancies were measured at the margin (µm) of each occlusal veneer. Silicone replicas were obtained to measure marginal and internal discrepancies (µm) that was evaluated with stereomicroscope at 35X magnification. All occlusal veneers were cemented to their corresponding abutments using adhesive resin cement. After 24 hours water storage and thermocycling for 5000 cycles at 55-5 °C, specimens were subjected to dynamic loading in a chewing simulator with 120.000 loading cycles. Then marginal discrepancies (µm) were evaluated after final cementation. The data were statistically analysed using Wilcoxon signed Rank test and three-way ANOVA test was used for detection of effect of material type and bonded substrate on dependant outcome. Results: After cementation, significantly higher marginal discrepancies were notes in comparison with before cementation. Restorative materials significantly affected on the marginal and internal adaptation. Conclusions: Occlusal veneer bonded to dentin with filling composite showed better marginal and internal adaptation than bonded to dentin with prepared cavity and bonded to dentin. Hybrid ceramic restoration provided superior marginal and internal adaptation than zirconia and lithium disilicate restoration.